1. Field of The Invention
This invention relates to a fluid catalytic cracking process. The invention also relates to the regeneration of inactivated fluid catalytic cracking catalyst by the oxidation of coke deposited thereon.
2. Description of Related Methods In The Field
The catalytic cracking of hydrocarbon feedstocks is well known. U.S. Pat. No. 4,304,659 to R. E. Pratt et al. incorporated herein by reference teaches a process wherein regenerated catalyst is fluidized in the lower portion of a riser transport line reactor and mixed with a hydrocarbon charge stock. Hydrocarbon conversion products including a fuel boiling range product, gas and coked catalyst are discharged from the upper end of the riser reactor into a reaction vessel. In the reaction vessel, coked catalyst is separated in a cyclone separator and passed to a stripping section where hydrocarbon vapors are steam stripped from the catalyst. The resulting coke contaminated catalyst, termed spent catalyst is collected in a spent catalyst standpipe and passed to a vertically arranged cylindrical regenerator vessel. The spent catalyst is passed substantially vertically downwardly by means of a catalyst entry nozzle into a fluidized dense phase catalyst bed. The fluidization is maintained by upwardly flowing oxygen containing regeneration gas introduced by a gas distributor into the lower portion of the dense phase catalyst bed contained in the bottom of the regenerator vessel. Regeneration gas is supplied in excess of that required for complete oxidation of coke as indicated by the analysis of oxygen in flue gas. Above the dense phase catalyst bed is a dilute phase bed wherein residual carbon is oxidized at a temperature higher than in the dense phase bed. Reactivated catalyst, substantially reduced in coke (0.15 wt% or less) is passed vertically upwardly by the fluidizing regeneration gas to an upper portion of the dilute phase bed and into a regenerated catalyst standpipe where it is collected for reuse in the riser reactor.
U.S. Pat. No. 4,443,551 to T. A. Lionetti et al. incorporated herein by reference teaches a regeneration gas distributor in the catalyst regenerator of a fluid catalytic cracking process. The distributor comprises a pair of horizontally disposed air rings. The lower air ring is supported adjacent the bottom of the regenerator vessel by a plurality of struts. High velocity air from a high pressure air manifold is passed through the air ring and ejected downwardly, thereby maintaining fluidization in the catalyst bed. An upper and outer air distribution ring is similarly positioned in the vessel. It is understood from this teaching that nozzle angle may vary depending on the particular air pressure and geometry of the vessel.
U.S. Pat. No. 4,150,090 to J. R. Murphy teaches an air distributor in a spent catalyst regenerator. The patent teaches introducing spent catalyst to a dense phase fluid bed. The catalyst is distributed steadily and evenly over the top of the catalyst bed. Air is distributed in the bed by a plurality of horizontally extending pipes on which are mounted branch pipes. Nozzles which pass air into the catalyst bed are mounted on the branch pipes. The distributor is designed to deliver air evenly into the fluid bed for migration upward to burn the coke evenly within the bed.
Fluidized cracking catalyst regeneration process and apparatus are described in U.S. Pat. Nos. 4,035,153 and 4,051,069 both to D. P. Bunn, Jr. et al. and U.S. Pat. Nos. 4,060,395 and 4,062,759 both to L. F. Castagnos, Jr. et al. U.S. Pat. No. 4,223,843 to R. S. Smith et al. teaches air distribution apparatus nozzle design.